The present invention is related to the use of specific cyclic and/or polymeric aryl-phosphines as flame retardants and to a method for reducing the flammability of organic material by incorporating into the material these specific cyclic and/or polymeric phosphines. Moreover, the invention is related to a polymeric composition containing a polymeric material and at least one of the specific cyclic and/or polymeric phosphines in an amount of from 1 to 15% by weight, based on the weight of the polymeric material. The invention also relates to a composition comprising at least one of the specific cyclic and/or polymeric phosphines and at least one polymerizable monomer.
Flame resistance is a significant property for organic materials, such as wood, primarily timber, paper, paperboard, textiles, flammable performance liquids and in particular polymeric materials. In some applications, flame resistance is given first priority due to the danger to human beings and material assets, for example in structural materials for airplane and motor vehicle construction and for public transportation vehicles. In electronic applications, flame resistance is necessary because the components may generate localized high temperatures. Therefore, a high level of flame/fire protection is warranted.
Accordingly, it has been customary to incorporate into organic materials and in particular into polymeric materials flame retardants.
The flame retardant market today is comprised of products which function to interfere with the combustion process by chemical and/or physical means. Mechanistically, these flame retardants have been proposed to function during combustion of an article either in the gas phase, the condensed phase or both.
The most common flame retardants thus far used commercially have been halogen containing compounds such as tetrabromobisphenol A, decabromodiphenyl oxide, de-cabromodiphenyl ethane, brominated carbonate oligomers, brominated epoxy oligomers, and poly(bromostyrenes). The organohalogens are proposed to generate halogen species (e.g. HX) which interfere in the gas phase with free radical organic “fuel” from the polymer substrate.
Generally, halogen containing fire retardants such as those listed above are considered to be safe and effective. However, there has been increasing interest to utilize halogen-free flame retarding substances. It is desirable for the materials equipped with these compounds to be able to meet the requirements of fire retardancy and to display the same or better properties, such as mechanical resistance, toughness, solvent and moisture resistance, etc. that is offered with the halogenated materials currently used.
Many different approaches have been investigated to flame retard organic polymers without the use of halogens (for recent reviews see: Journal of Fire Sciences 24, 345-364, 2006; Journal of Fire Sciences 22, 251-264, 2004; Polymer International 54, 11-35, 2005; Polymer International 54, 981-998, 2005).
One general approach to using non-halogen flame retardants in organic polymer materials is by the use of phosphorus based flame retardants. In polyamide systems, red phosphorus has been well-established in glass-reinforced polyamide 66 resins (Weil, E. D. Red Phosphorus—an Update, Paper in 11th Annual BCC Conference of Flame Retardancy, Jun. 1-3, 1998). The color of the final product and the handling of red phosphorus are concerns with this approach that need to be dealt with. More recently, for polyamides, the uses of various salts of dialkylphosphinic acids have been promoted by Clariant under the Exolit® name.
The use of melamine based materials has been used in certain polyamide resin systems. For unreinforced polyamide 66, melamine cyanurate is used (Stern and Horacek Intern. J. Polymeric Mater. 25, 255-268, 1994; Casu, Camino, et al., Polym. Degrad. Stabil., 58, 297-302, 1997). This material is believed to work by providing enhanced non-burning drips and also by undergoing an endothermic decomposition to produce a non-combustible vapour. However, melamine cyanurate has difficulty achieving a V-0 flame retardant classification when glass-filled polyamide 66 is used. In that case, melamine pyrophosphate has been shown to be effective at a higher 28% loading with a 20% glass system (Kasowski, et al., New Advances in Flame Retardant Technology, Paper presented at FRCA, p 23, 1999).
In polycarbonate blends, various aromatic phosphates are usually the products of choice. Standard example materials would be resorcinol bis(diphenyl phosphate) or bisphenol A bis(diphenyl phosphate). In polyesters, a wide variety of phosphorus-based materials has been investigated (Polymer International 54, 981-998, 2005). These materials range from phosphine oxides to phosphates and all have certain advantages and disadvantages.
Another approach to enhance flame retardancy is to add flame retardant adjuvants to organic materials, in particular to polymeric materials, which prevent dripping during the fire. This is most commonly accomplished by adding low levels of polytetrafluoroethylene. Dripping during combustion is the process of the separation of parts of the polymer from the matrix in the shape of droplets. Most often, the droplets are flaming and are imposing tremendous danger for fire spread. A further common measure to add fillers such as talc in large amounts to the polymer, with some negative consequences on the mechanical properties. Fillers sometimes used include calcium carbonate, magnesium carbonate, zinc borate, silicates, silicones, glass fibres, glass bulbs, asbestos, kaolin, mica, barium sulfate, calcium sulfate, metal oxides, hydrates and hydroxides such as zinc oxide, magnesium hydroxide, aluminum trihydrate, silica, calcium silicate and magnesium silicate.